The present invention relates to a packet-transmitting system for performing code-division multiplexing on a stream of data packets and parallel transmission of data packets.
A packet-transmitting system is known which comprises a transmitting station and a receiving station. In the transmitting station, error-correction codes are added to a stream to data packets, and the data packets are modulated and transmitted from the antenna. In the receiving station, the antenna receives signals of all bands. The signals are demodulated and subjected to error correction, thereby reproducing the data packets. The packets are supplied to a packet-selecting circuit, which selects the packets having the ID the user has designated.
Recently, digital broadcasting employing the conventional packet-transmitting system has been developed to broadcast a plurality of programs at the same time. In the packet-transmitting system, the programs are transmitted in the form of a stream of data packets from the transmitting station to the receivers. At each receiver, the user can enjoy only one program at a time in most cases. Nonetheless, the receiver receives all data packets and processes them all. To process many data packets, the receiver must have a large-scale circuit configuration and consume much power. This inevitably increases the manufacturing and running costs of the receiver.
There is another problem with the conventional packet-transmitting system. Since all packets are modulated altogether, the parameters of error- correction codes or the characteristics of signals cannot be changed for each packet (program). Hence, the conventional packet-transmitting system cannot accomplish broadcasting in various manners desired.
The present invention has been made in view of the foregoing. The object of the invention is to provide a packet-transmitting system in which the receiver receives only the packet the user needs and the parameters of error-correction codes or the characteristics of signals can be changed for each packet (program) to achieve broadcasting in various manners desired.
(1) To achieve the object, a packet-transmitting system has at least one control-signal transmission channel and a plurality of data-signal transmission channels. The system comprises a transmitter apparatus and a receiver apparatus. The transmitter apparatus includes: packet-allocating section for receiving a stream of packets and allocating groups of packets to the data-signal transmission channels; time-dividing/multiplexing section for receiving packet-group data representing the packets allocated to each data-signal transmission channel by the section and for time-dividing and multiplexing the packet-group data to the control-signal transmission channel; and multiplexer/adder section for multiplexing a signal in the control-signal transmission channel and signals in the data-signal transmission channels in parallel, thereby to generate signals to be transmitted. The receiver apparatus includes: signal-distributing section for distributing the signals to a plurality of channels; group-data acquiring section for reproducing the signal in the data-signal transmission channel from a signal distributed to any channel by the signal-distributing section, thereby to acquire group data about the data-signal transmission channels; channel-selecting section for selecting a data-signal transmission channel to which a packet group designated is allocated, in accordance with the group data acquired by the group-data acquiring section; and selected-channel reproducing section for reproducing a signal in the data-signal transmission channel selected by the channel-selecting section, from the signals in some of the transmission channels to which the signal-distributing section has distributed the signals and for extracting only the packets of the group designated, the signals in some transmission channels not having been used in the group-data acquiring section.
(2) In the packet-transmitting system described in the paragraph (1), the packet-allocating section may allocate the packets of the same group to a plurality of data-signal transmission channels, and the time-dividing/multiplexing section may time-divide and multiplex the packets thus allocated, as the packet-group data, to the control-signal transmission channel.
(3) In the packet-transmitting system described in the paragraph (1), the group data may represent packet identifiers that the packets have.
(4) In the packet-transmitting system described in the paragraph (1), the multiplexer/adder section may multiplex the signal in the control-signal transmission channel and the signals in the data-signal transmission channels, by section of a code dividing/multiplexing system.
(5) In the packet-transmitting system described in the paragraph (1), the transmitter apparatus may comprise time-management data correcting section for finding a difference between the timing of each packet to be allocated by the packet-allocating section and the timing of the same packet allocated by the packet-allocating section, and for correcting time-management data contained in the packet, in accordance with the difference.
(6) In the packet-transmitting system described in the paragraph (1), the transmitter apparatus may comprise scramble section for scrambling the packets in the data-signal transmission channels and time-dividing a scramble key to one of the data-signal transmission channels.
(7) In the packet-transmitting system described in the paragraph (6), the scramble section may eliminate a difference between a signal delay in the transmission channel for transmitting the scramble key and a signal delay in the transmission channels for transmitting the packets, before the scramble key and packets are transmitted.
(8) According to this invention there is provided a transmitter apparatus for use in a packet-transmitting system having at least one control-signal transmission channel and a plurality of data-signal transmission channels. The transmitter apparatus comprises: packet-allocating section for receiving a stream of packets and allocating groups of packets to the data-signal transmission channels; time-dividing/multiplexing section for receiving packet-group data representing the packets allocated to each data-signal transmission channel by the packet-allocating section and for time-dividing and multiplexing the packet-group data to the control-signal transmission channel; and multiplexer/adder section for multiplexing a signal in the control-signal transmission channel and signals in the data-signal transmission channels in parallel, thereby to generate signals to be transmitted.
(9) According to the present invention there is provided a receiver apparatus for use in a packet-transmitting system having at least one control-signal transmission channel and a plurality of data-signal transmission channels. The receiver apparatus is designed to receive signals generated by allocating groups of packets to the data-signal transmission channels, by time-dividing and multiplexing, the control-signal transmission channel, packet-group data allocated to each of the data-signal transmission, channel and by multiplexing a signal in the control-signal transmission channel and signals in the data-signal transmission channels in parallel. The receiver apparatus comprises: signal-distributing section for distributing the signals to a plurality of channels; group-data acquiring section for reproducing the signal in the data-signal transmission channel from a signal distributed to any channel by the signal-distributing section, thereby to acquire group data about the data-signal transmission channels; channel-selecting section for selecting a data-signal transmission channel to which a packet group designated is allocated, in accordance with the group data acquired by the group-data acquiring section; and selected-channel reproducing section for reproducing a signal in the data-signal transmission channel selected by the channel-selecting section, from the signals in some of the transmission channels to which the signal-distributing section has distributed the signals and for extracting only the packets of the group designated, the signals in some transmission channels not having been used in the group-data acquiring section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.